| dc.description.abstract | In many cases, estimation of the peak discharge is the primary goal of hydrologic modeling. We employed a dataset of 1,648 rainfall-runoff events in 104 watersheds in Texas to explore the peak rate factor (PRF) of 484 recommended by the Natural Resources Conservation Service (NRCS) for determining peak discharges with the unit hydrograph method, as well as the PRF’s dependency on watershed and storm characteristics. For each event, a unit hydrograph – assumed to follow a two-parameter Gamma distribution – was determined by deconvolving the direct runoff hydrograph with the excess rainfall hyetograph. Results showed PRFs reaching up to 2264 in Houston watersheds with a median of 135, and PRFs up to 2559 with a median of 329 for the rest of Texas. It was also found that the recommended PRF of 484 falls between the 75th and 90th percentile of the 1043 events analyzed in all regions except Houston, and is above the 98th percentile in all 605 events analyzed in Houston. Statistical analysis further proved that PRFs in Houston watersheds are significantly different from the rest of Texas.
To estimate the dependency of the PRF on watershed and storm parameters, regression analysis was performed, and results showed that the PRF is primarily dependent on the watershed’s geomorphology and the main channel slope; however, its dependency on the main channel slope was largely influenced by Houston watersheds, which are characterized by flat slopes. When regression analysis only focused on non-Houston watersheds, statistical analysis only showed dependency on the watershed’s geomorphology and not its slope. This dependency, however, although statistically significant, explains only marginally the PRF variability. It is therefore recommended that for practical applications, and in the absence of high-quality rainfall-runoff data, constant PRFs of 135 and 329 be used Houston watersheds and non-Houston Texas watersheds, respectively. | |
